Mosquitoes are disease vectors for human beings and animals, carrying malaria, heartworm, dengue fever, encephalitis, yellow fever and West Nile virus, and causing greater than 1 million human deaths around the world, every year. Health concerns and discomfort related to insect bites and stings have led to widespread use of insecticides and repellent products. Commercially available insecticides commonly include toxic active ingredients which act against the target pests. However if used in relatively confined environments and delivered as aerosol sprays these products can become toxic to humans and treated animals. Various undesirable side effects may include immediate or delayed neurotoxic reactions and/or suffocation. The noxious odor alone can cause headaches or nausea in some individuals. These adverse side effects are exacerbated when such compositions come in contact with persons of increased sensitivity, or persons of small body mass such as children or babies.
Therefore efforts have been made to develop insecticidal compositions non-poisonous to humans and pets. These non-poisonous insecticidal compositions available heretofore have had limited efficacy. Furthermore, although insecticides, which kill the target pests, are usually the quickest forms of treatment, they kill not only the undesired insects, but beneficial insects as well. Insect repellents may offer a compromise that minimizes disease and discomfort in animals, without disrupting the natural balance of insect populations. Several existing repellents are presented in Table 1.
TABLE 1Commonly used repellentsMole-cularNameMoleculemassFormulaDiethyl- toluamide (DEET)191.13C12H17NO Picaridine229.17C12H23NO3 Benzyl benzoate212.08C14H12O2 Coumarin146.15C9H6O2
However, when used at concentrations effective to repel arthropod pests, existing repellents may also have toxic or otherwise undesirable consequences. Accordingly, there is a need for new formulations capable of effectively repelling pests, including insects, from animals, plants and building structures, and having improved safety and efficacy profiles. The formulations should be long lasting and of lesser toxicity than traditional repellents.
One possible solution to the problem may be the use of polymer-based colloidal particles, which have been largely used as solid support or carrier in numerous biomedical applications: latex or hybrid particles for in vitro biomedical diagnosis, biodegradable nanocapsules for in vivo drugs delivery (i.e. therapy), and in cosmetics. Biodegradable particles are particularly useful for therapy because they can be targeted to particular organs, tissues, cells or intracellular compartments via surface functionalization. Moreover, the use of active ingredient AI-loaded nanoparticles allows for both low-dose, continuous drug release, and local targeting, which together significantly reduce the severity of side effects as compared to, for example, those associated with systemic administration of the same AI.
TABLE 2Insect repellent formulations described in the literature,AI: Active Ingredient; DEET: N,N-diethyl-m-toluamideFormulationFormAI% AIprocessReferenceMicroparticlesDEET15% w/wInterfacial[1]precipitationMicroparticlesLimonella oil30% v/vCoacervation[2]Gel emulsionDEET10% w/wEmulsification[3]NanoemulsionCitronella oil20% w/wHigh pressure[4]homogenizerNanoemulsionEssential oils25% w/wHigh pressure[5]homogenizerSolid lipidDEET10% w/wEmulsification[6] [7]basednanoparticlesOne way to produce AI-loaded nanoparticles is via a process called “nanoprecipitation”. U.S. Pat. No. 5,049,322 [8] (to CNRS) discloses a “ . . . process for the preparation of dispersible colloidal systems in the form of spherical particles of the vesicular type and of a size less than 500 nm (nanocapsules), the wall of which is constituted by a substance A having film-forming properties and the core by a liquid substance B capable of being encapsulated by the substance A, comprising: combining (1) a first liquid phase consisting essentially of a solution of the substances A and B in a solvent for the substances A and B or in a mixture of solvents for the substances A and B, and (2) a greater amount of a second liquid phase consisting essentially of a non-solvent or a mixture of non-solvents for the substances A and B and including one or more surfactants, the solvent or the mixture of solvents of the first phase being miscible in all proportions with the non-solvent or mixture of non-solvents of the second phase, comprising a core of said liquid substance B surrounded by a layer of said substance A.”
Upon addition of the organic phase into the aqueous phase and slow mechanical stirring, the nanoparticles are formed instantaneously by the rapid diffusion of the solvent in the aqueous phase. The latter is then removed by evaporation under reduced pressure. Acetone, Ethanol or their mixture are widely used as organic phase. The formation mechanism of the nanoparticles by this technique is explained by transitory interfacial turbulence due to the diffusion of organic solvent in water phase. The conditions to obtain nanoparticles should include the mutual and the total miscibility between solvents of the two phases and the fact that the mixture of the two solvents must be a poor solvent of the chosen polymer. Nanoprecipitation uses small quantities of surface-active agents, is rapid, and can easily be performed at industrial scale. However, this method is not indicated for the encapsulation of AI with little to no water-solubility. Further, the chosen organic solvent should be miscible in all proportions with the water phase, and the miscibility should be rapid in order to lead to a rapid nucleation process. FIG. 1 presents an illustration of the nanoprecipitation process.
The polymer matrix forming the particles is able to encapsulate basic organic molecules (i.e. therapeutic agents), organic macromolecules (lipids, carbohydrates), biomacromolecules (nucleic acids, proteins and peptides), metals, contrast agents, oils, radiolabeled elements, and the like. The formulation recipe choice is driven by the targeted application and more specifically, the desired characteristics as regards drug release profile and physicochemical stability. Polymer based nanoparticles have been a focus of numerous studies since 1980 [9]. The technology of nanoparticles offers many advantages, such as the solubilization of lipophilic molecules, increased bioavailability, and the protection of AI against physical, chemical, and biological degradations during storage and use.
The nanoparticles intended for a dermal use offer several advantages, mainly in comparison with the emulsions and the liposomes. The AI-loaded nanoparticles are able to cross the surface layers of the stratum corneum and to diffuse in the basal layers of the skin to specifically release the AI. This penetration into the deeper layers widens the action space of the AI and it protects the AI against rapid elimination by simple friction. The solid matrix nature controls the AI release through the skin. The occlusive effect caused by the deposition of nanoparticles increases the tank effect of the cornea layer and increases percutaneous absorption [10]. For a cutaneous application, the nanoparticle nature and size will condition the routing of the AI until the target site (pilous follicles, stratum corneum, epidermis, etc.) improving the tissue tolerance. In addition, by modulating the properties of nanoparticle surface, the composition and the medium, the desired release model of the AI and its biodistribution can be controlled.
The major characteristic of nanoparticle suspension preparation is the size of the formulated objects. Nanoparticle size depends in particular on solvent nature, active molecule concentration, organic phase/aqueous phase ratio, polymer, surfactant nature and percentage. Particle physicochemical characteristics can be specifically modified by judicious selection of polymer and surfactant properties (e.g. surface charge, porosity, biodegradability, etc.). Nanometric size and narrow size distribution lead to long term colloidal stability. A charged surface increases particle stability, and electrostatic surface modifications (with partially oppositely charged compounds) can contain target-specific ligands for improving passive and active targeting. Finally, the choice of solvent must be such that modifications of the physical properties of nanoparticles may occur. For example, a highly water miscible solvent (e.g., Dimethyl formamide, DMF) tends to diffuse into water faster than a solvent with lower water miscibility (e.g., acetone, tetrahydrofuran). The replacement of acetone by tetrahydrofuran is known to yield a decrease in particle size [11]. Polymers can be acquired commercially or synthesized from selected monomers or modified from preformed polymer, which allows for fine-tuning of the physicochemical properties of the final nanoparticles [12]. The particle size typically shows a linear correlation with the polymer concentrations because the number of particles remains essentially unchanged at the fixed condition [13].
Several factors impact particle size and size distribution. In general, a highly hydrophobic polymer in a highly water miscible solvent will nucleate very quickly and have a relatively smaller particle size. Surfactant presence in the formulation is a size control parameter; the nature and percentage allow achievement of a given particle size with a narrow size distribution. Finally, stirring process during the pouring of one phase in the other does not change the mean particle size, but does have tendency to decrease the polydispersity of the particles.
Active molecule hydrophobicity effect on the size and encapsulation efficiency of Indomethacin (hydrophobic) and doxorubicin (hydrophilic) formulated by nanoprecipitation using polylactide polymer shell were compared [14]. As example, Indomethacin-loaded nanoparticles provide a particle size of 190 nm with 80% of entrapped active molecule, against 290 nm and 50% of entrapped active molecule for Doxorubicin.
A major disadvantage of commercial pest repellent formulations has been the short duration of efficacy. Nanoparticle formulations could provide a useful solution, and as the above-described technologies have not yet been applied to the problem of pest repellency, it is an object of the instant invention to provide nanoparticle/AI formulations with improved safety and efficacy profiles, as compared with existing arthropod repellent formulations.
It is expressly noted that citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention. Any foregoing applications, and all documents cited therein or during their prosecution (“application cited documents”) and all documents cited or referenced in the application cited documents, and all documents cited or referenced herein (“herein cited documents”), and all documents cited or referenced in herein cited documents, together with any manufacturer's instructions, descriptions, product specifications, and product sheets for any products mentioned herein or in any document incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention.